1. Field of the Invention
This invention relates to pyrrolo[1,2-a]pyrroles, and especially to the synthesis of 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylic acid and its dialkyl esters.
2. Background to the Invention
5-Aroyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acids, also known as 5-aroyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acids, of formula I, and the ##STR2## pharmacologically acceptable salts and esters thereof, are useful as analgesic, anti-inflammatory, and anti-pyretic agents for mammals, including man. They are also smooth muscle relaxants. Two exemplary compounds under clinical study in man are ketorolac, 5-benzoyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1carboxylic acid, (I, Ar.dbd.C.sub.6 H.sub.5), and anirolac, 5-p-anisoyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid, (I, Ar.dbd.p--CH.sub.3 O--C.sub.6 H.sub.5), both disclosed in U.S. Pat. No. 4,089,969 to Muchowski et al. Other compounds, where the 5-aroyl substituents are substituted or unsubstituted benzoyl, furoyl, thenoyl, and pyrroyl, and where the 6-position on the pyrrolo-pyrrole nucleus is optionally substituted by lower alkyl or halogen, and uses thereof, are also disclosed in a series of patents assigned to Syntex (U.S.A.) Inc., beginning with U.S. Pat. No. 4,089,969, and including U.S. Pat. Nos. 4,087,539; 4,097,579; 4,140,698; 4,232,038; 4,344,943; 4,347,186; 4,458,081; 4,347,187; 4,454,326; 4,347,185; 4,505,927; 4,456,759; 4,353,829; 4,397,862; 4,457,941; and 4,454,151. U.S. Patents Nos. 4,511,724 and 4,536,512, assigned to Merck & Co., Inc., disclose 5-(substituted pyrrol-2-oyl)-2,3-dihydro-1H-pyrrolo-[1,2-a]pyrrole-1-carboxylic acid derivatives and 5-(2,3-dihydro-1H-pyrrolo[1,2-a]pyrrol-2-oyl)-2,3-dihydro-1H-pyrrolo[1,2-a ]pyrrole-1-carboxylic acid derivatives, respectively; while U.S. Pat. No. 4,533,671, also assigned to Merck & Co., Inc., discloses 5-(2,3-dihydro-1H-pyrrolo[1,2-a]pyrrol-2-oyl)-2-pyrrole-alkanoic acids and analogs.
Various methods for the preparation of these pyrrolo-pyrroles are exemplified in the patent and chemical literature, and many proceed through a common intermediate, 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylic acid, (II, R.dbd.H), or its dialkyl ester; ##STR3## the preparation of which from dimethyl 1,3-acetone-dicarboxylate, ethanolamine, and a haloacetaldehyde is disclosed in, for example, U.S. Pat. No. 4,089,969, which is incorporated herein by reference.
The reaction scheme set forth in that patent: ##STR4## includes the reaction of equimolar amounts of ethanolamine (III) and dimethyl 1,3-acetonedicarboxylate (IV) to form a solution of the hydroxyenamine (V), which is then treated, preferably in situ, in a suitable organic solvent (aprotic solvents such as acetonitrile, dichloromethane, etc. are exemplified), under anhydrous conditions, with a 2-haloacetaldehyde at elevated temperatures to produce the N-(2-hydroxyethyl)pyrrole (VI). Compound VI is esterified with methanesulfonyl chloride to produce the mesylate (VII), which is optionally converted to the N-(2-iodoethyl)pyrrole (VIII) by reaction with sodium iodide. Either of compounds VII and VIII may be converted to dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1,7-dicarboxylate (II, R.dbd.CH.sub.3) by treatment with sodium hydride in dimethylformamide. The thus-formed dimethyl 2,3-dihydro-1H-pyrrolo[1,2-a]-pyrrole-1,7-dicarboxylate may then be selectively 7-decarboxylated and 5-aroylated, by methods such as those described in the previously-cited patents and in U.S. Pat. No. 4,496,741 to Doherty, to yield a 5-aroyl-2,3-dihydro-1H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid (I). A similar process, involving the reaction of ethanolamine, dimethyl 1,3-acetonedicarboxylate, and a halomethyl alkyl ketone, bypasses the hydroxyenamine (V) and produces the 4-alkyl analog of (VI) directly. That compound may be converted to the pyrrolo-pyrrole in the same manner as for the 4-unsubstituted compound previously described.
Processes for the preparation of 5-aroyl-N-R-pyrrole-2-acetic acid, where R is H, lower alkyl, or benzyl, and analogous compounds are disclosed in U.S. Pat. Nos. 3,752,826; 3,865,840; and 3,952,012 to Carson. They include, for the 4-alkyl substituted but not for the 4-unsubstituted compounds, the reaction between a lower alkylamine, a di(lower alkyl) 1,3-acetonedicarboxylate, and a chloromethyl lower alkyl ketone, "preferably in an aqueous medium", followed by pouring into ice-cold hydrochloric acid, to produce compounds of formula IX, where each of R, R', and R" is lower alkyl. ##STR5## A similar process for the 4-unsubstituted compounds (IX, R'.dbd.H) using chloroacetaldehyde is disclosed in U.S. Pat. No. 4,048,191 to Carson.
U.K. Published Application No. 2 034 304 A, assigned to Mallinckrodt, Inc., discloses a process for the preparation of compounds of formula IX, wherein R' may be hydrogen or alkyl, by either (a) forming a two-phase reaction medium of an aqueous solution of the alkylamine and an inert, water-immiscible organic solvent, and adding the dicarboxylate and ketone (or aldehyde) substantially simultaneously, or (b) adding the dicarboxylate and ketone substantially simultaneously, with the ketone in excess, to an aqueous alkylamine. Preferably, dicarboxylate and excess ketone are added to an alkylamine dispersion.
A number of patents assigned to Ethyl Corporation, including U.S. Pat. Nos. 4,565,878; 4,565,879; 4,374,255; 4,388,468; 4,383,117; 4,455,433; and 4,333,878, disclose other modifications of the Carson syntheses. U.S. Pat. No. 4,565,878 discloses the addition of a water-immiscible co-solvent [a halogenated hydrocarbon of good solubility for both the di(lower alkyl) 1,3-acetonedicarboxylate and the product] to the mixture of chloromethyl lower alkyl ketone, dicarboxylate, and aqueous lower alkylamine. U.S. Pat. No. 4,565,789 discloses the use of an aromatic hydrocarbon as the co-solvent. U.S. Pat. No. 4,374,255 discloses the addition of "a solids formation inhibiting amount of a lower alkanol" to the ketone/dicarboxylate/-aqueous alkylamine mixture. The reaction is normally carried out in the presence of a co-solvent as in U.S. Pat. Nos. 4,565,878 or 4,565,879. U.S. Pat. No. 4,388,468 discloses a two-stage process in which (a) the ketone is added to a pre-mixed cooled solution of the alkylamine and the dicarboxylate in a suitable solvent (e.g. aromatic hydrocarbons, chlorinated hydrocarbons, water, or mixtures thereof) at a temperature less than 60.degree. C., followed by (b) heating the reaction mixture to 70.degree.-100.degree. C. U.S. Pat. No. 4,383,117 discloses the use of an anhydrous lower alkylamine instead of an aqueous solution, and the use of a single-phase non-aqueous reaction medium. U.S. Pat. No. 4,455,433 discloses the addition of "a yield-enhancing amount of an acid having a dissociation constant of at least 1.3.times.10.sup.-5 at 25.degree. C." to a ketone/dicarboxylate/(preferably anhydrous) lower alkylamine mixture, preferably in an organic solvent. U.S. Pat. No. 4,333,878 discloses the synthesis of compounds of formula IX by the reaction of an enamine (X) ##STR6## with a 2-carboxy-1-nitroalkane (XI, R*.dbd.lower alkyl, tolyl, or benzyl). The enamine may be prepared by the reaction of a di(lower alkyl) 1,3-acetonedicarboxylate with a lower alkylamine in "a suitable solvent, such as ethanol or methanol", followed by evaporation of the solvent and heating to dehydrate the thus-formed carbinolamine to the corresponding enamine.
Albert et al., in U.S. Pat. No. 4,363,918, disclose the synthesis of compounds of formula IX where R is lower alkyl, R' is hydrogen or lower alkyl, and R" is H by the reaction of 1,3-acetonedicarboxylic acid with ClCH.sub.2 COR and a lower alkylamine, preferably by the slow addition of an aqueous solution of the lower alkylamine to an aqueous solution of the acid, followed by slow addition of the 1-chloro-2-alkanone, with both additions preferably occurring below 20.degree. C. or lower.
European Published Applications Nos. 92 487 and 105 664, assigned to Montedison S.p.A., disclose the preparation of compounds of formula IX wherein R is CH.sub.3 and R" is H, and R' is CH.sub.3 (EP92487) or H (EP105664) by the reaction of 1,3-acetonedicarboxylic acid or an alkali metal salt thereof with methylamine and a halo (ketone or aldehyde) in aqueous solution, preferably by adding the haloketone to an aqueous mixture of the methylamine and the dicarboxylic acid.